The present invention relates to component television video monitors, and more particularly to a composite signal-limit indicator for such a component monitor to verify that the processing or signal creation in other component video formats does not violated signal dynamic range limitations when encoded into a composite signal.
Existing component television video signal monitors, such as the WFM-300A manufactured by Tektronix, Inc. of Wilsonville, Oreg., United States of America, have the ability to detect color gamut violations, as indicated by U.S. Pat. No. 4,707,727 issued Nov. 17, 1987 to Bruce J. Penney entitled "Apparatus for Providing an Indication That a Color Represented by a Y, R-Y, B-Y Color Television Signal is Validly Reproducible on an RGB Color Display Device". The encoded color components Y, R-Y, B-Y are transformed into the primary color components RGB and input to two sets of comparators, one set having as a reference level the maximum value (700 mV) and the other set having as a reference level the minimum value (0.0 V). The outputs of the comparators are input to an OR gate so that, if any one of the primary color components are above or below the maximum or minimum values, a gamut error signal is produced. The gamut error signal is used to drive an LED on a front panel as a gamut error indicator.
The 500 Series Waveform Monitors/Vectorscopes manufactured by Magni Systems, Inc. of Beaverton, Oreg. also provide a gamut indication. A separate output for each comparator is provided for display so that the primary color component and direction (plus or minus) of the gamut error are displayed.
Signals in various component formats need to be converted to RGB to verify that the processing or signal creation in these formats has not violated the signal dynamic range limitations in the RGB format, referred to as component gamut violation. Since the signal very often has to be converted to composite NTSC or PAL for distribution, there is the additional problem of composite signal level violations. When the component signals are encoded into a composite signal by passing them through a properly adjusted composite encoder, the output magnitude may exceed the allowed composite signal levels even though the component input is within the RGB formal limits. The traditional way of resolving this is to use an additional signal monitor at the output of the composite encoder to monitor the composite signal levels. This may be acceptable unless color gamut adjustments are being made on a component system and it is to be encoded into a composite format elsewhere. Also the value of this technique is only as good as the encoder accuracy. However there is a growing need to monitor component formats such as RGB and Y,Pb,Pr either in digital or analog form and verify that they are within the composite signal level limits.
What is desired is the ability to detect or display the composite signal level violations on a component monitor.